initial timing experiment

phy121

Your 'initial timing experiment' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.

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Initial Timing Experiment

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In this experiment you will use the TIMER program, a hardcover book, a cylinder or some other object that will roll along the book in a relatively straight line, and a ruler or the equivalent (if you don't have one, note the RULERS link on the Assignments page).

Place the book on a flat level tabletop.  You will prop one end of the book up a little bit, so that when it is released the object will roll without your assistance, gradually speeding up, from the propped-up end to the lower end.  However don't prop the end up too much.  It should take at least two seconds for the ball to roll down the length of the book when it is released from rest.

Then reverse the direction of the book on the tabletop, rotating the book and its prop 180 degrees so that the ball will roll in exactly the opposite direction.  Repeat your measurements.

In the box below describe your setup, being as specific as possible about the book used (title, ISBN) and the object being used (e.g., a solid glass marble, a small can of tomato paste (full or empty?), a ball-point pen), and what you used to prop the object up (be as specific as possible).   Also describe how well the object rolled--did it roll smoothly, did it speed up and slow down, did it roll in a straight line or did its direction change somewhat?

Note:  Don't trust this form.  Compose your answer in Notepad or a word processor, saving it every few minutes, then copy and paste it into the box.  Power could surge, your computer could malfunction, in any of a number of ways the work you put into this form could be lost.  Compose it elsewhere and keep a copy.

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Using Giancoli's Sixth Edition of PHYSICS, ISBN 9780130606204, and an empty Diet Coke can, and a PaperMate Classsic # 2 pencil, I:

1. Laid the book flat on my kitchen table, then propped up the top end with the number two pencil. The low end of the book was 3.8cm from the table top, and the high end was 4.6 cm from the table top. The book itself was 28.1 cm long.

2. Held the can at the top of the incline, and released it while simultaneously starting the timer. The can rolled smoothly down the book in a fairly straight line.

3. Stopped the timer when the can reached the bottom edge of the book.

I repeated these steps three times, recording the results of the time it took travel the length of the book from rest.

I repeated this 3 times, then rotated the book 180 degrees and replaced the prop. I repeated the experiment with the book in the opposite direction.

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In the box below report your data.  State exactly what was measured, how it was measured, how accurately you believe it was measured and of course what the measurements were.  Try to organize your report so the reader can easily scan your data and see any patterns that might occur.

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Timer started when can released, stopped when can reached lower edge of book.

Book top at left end of table Book top at right end of table

2.417969 2.335938

2.226563 2.488281

2.296875 2.511719

I tried very hard to be consistent with starting and stopping the timer, but my concerns about accuracy lie in my ability to start the timer and release the can simultaneously.

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Using your data determine how fast the object was moving, on the average, as it rolled down the incline.  Estimate how accurately you believe you were able to determine the object's average speed, and give the best reasons you can for your estimate of the accuracy.

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Book top at left end: Avg time to roll down book: 2.313802333

‘ds / ‘dt = avg velocity

28 cm / 2.313802333s =12.10129301 cm/s, or about 12.1 cm/s

Book top at right end: Avg time to roll down book: 2.445312667

28 cm / 2.445312667 =11.45047845, or about 11.5 cm/s

It is difficult to determine how accurate my results are, because I don’t know how accurate my reflexes are. I would guess 3 significant figures.

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Devise and concuct an experiment to determine whether or not the object is speeding up as it rolls down the incline.  If you have set the experiment up as indicated, it should seem pretty obvious that the object is in fact speeding up.  But figure out a way to use actual measurements to support your belief.

Explain how you designed and conducted your experiment, give your data and explain how your data support your conclusions.

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To determine whether the object was speeding up, we could draw a line half way down the incline of the book. Using the timer, we could measure the time from release to the line, then from the instant the can crosses the line to the edge of the book. (This would need to be done in two rolls, both from rest at the top of the book.) We would need to do at least 3 trials of each. We could determine average velocity for each distance, and then compare the average velocity of the can in the first half of the incline to the average velocity on the second half of the incline. If the second half velocity is faster than the first half, we have proven that the can sped up as it travelled down the incline.

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Your instructor is trying to gauge the typical time spent by students on these experiments.  Please answer the following question as accurately as you can, understanding that your answer will be used only for the stated purpose and has no bearing on your grades: 

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30 min

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You may add optional comments and/or questions in the box below.

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&#Your work looks very good. Let me know if you have any questions. &#